1. Field of the Invention
This invention relates to antistatic polyester film and method for the production of the same. More particularly, this invention relates to antistatic polyester film having a stable, low surface resistivity and having excellent transparency, evenness, slipperiness and anti-blocking property as well as to method for the production of the same.
2. Prior Arts
Plastic film such as biaxially oriented and thermoset-polyester film is excellent in mechanical properties, heat resistance, gas shielding property, chemical resistance, etc. but the polyester film has a high surface resistivity as high as 10.sup.14 to 10.sup.17 .OMEGA./.quadrature. and is readily charged, resulting in that it tends to arise troubles of adsorbing foreign matters when said film has been used in magnetic recording media or electronic materials.
Heretofore, there have been known various methods for preventing the charge of film such as a method in which an antistatic agent such as lithium dodecylbenzenesulfonate is kneaded in a base polymer, or a method an antistatic agent having a low molecular weight is coated on a surface of a film. However, the former method involving the kneading of an antistatic agent generally results in a poor compatibility between the antistatic agent and the polyester. Hence, if the antistatic agent is kneaded in the polyester in amounts enough to exhibit the antistatic property, the resulting film becomes opaque, and therefore it is disadvantageous to use the film in fields where transparency of film is required, for example as an OHP film. On the other hand while the method of coating an antistatic agent on a surface of a polyester film is excellent in transparency of the film, the antistatic agent is viscous to some extent due to its low molecular weight, and therefore films tend to be blocking with each other. Also, when only an antistatic agent is coated on a surface of a polyester film, the antistatic agent tends to peel off the surface of the film due to poor adhesion between the antistatic agent and the base film, results in disadvantage that the antistatic effect decreases. Also, the coated film has a defect that tapes or the like do not adhere thereon.